What is that, you ask?
Well, the story goes that a police department once hit upon a perfect way to get a confession. They took a colander, attached it to a copier machine with some wires, and made a suspect wear the colander. Every time he said something that the cops figured was a lie, they pushed the print button on the copier, which would then spit out a piece of paper saying HE’S LYING.
The suspect eventually confessed.
It’s so totally an urban legend: I would have linked to Snopes, but they won’t let you cut and paste key passages, so screw them.